The D-vitamins (i.e., vitamin D.sub.3 and vitamin D.sub.2) are well-known for their regulatory effect on calcium and phosphorus metabolism. In the normal animal these compounds promote intestinal calcium transport and raise blood calcium and phosphorus levels. Presumably because of their regulatory function in mineral metabolism, the D-vitamins, when administered in superphysiological doses can be highly toxic to the animal. This toxic effect is well-known and has been exploited for some time through the use of vitamin D.sub.3 or D.sub.2 as rodenticidal agents. However, rodenticidal applications of vitamin D.sub.3 and D.sub.2 require relatively large amounts of these compounds which often lead to bait-shyness or bait refusal by the rodent and hence reduce the effectiveness of these compounds in rodent control, while at the same time aggravating the problems associated with secondary poisoning.
To avoid these problems the use of vitamin D analogs, e.g., 1.alpha.-hydroxyvitamin D.sub.3, 1.alpha.-hydroxyvitamin D.sub.2 and 1,25-dihydroxyvitamin D.sub.3, compounds showing much higher rodenticidal activity than D.sub.3 itself, have been proposed (U.S. Pat. No. 4,035,493). However, the relatively high cost of preparation of these compounds in pure form may, as a practical matter, limit their application in the field.